In the 1980s, fossil record research showed a curious cycle: Every 27 million years, Earth hosted a mass extinction. Some scientists suggested that a dim star dubbed Nemesis was in a deadly dance with our sun, periodically kicking comets out of the distant Oort Cloud to shower our planet with destruction. Morbidly fascinating as it may be, the authors of a new study argue that this “death star” theory doesn’t hold up.

The cyclical extinctions do make a solid pattern, say Adrian Melott of the University of Kansas and Richard Bambach of Smithsonian Institution Museum of Natural History, whose paper is available through arXiv.org. The two have gone back in the record to 500 million years ago, further than any other researchers, and have confirmed the 27 million year cycle at a 99 percent confidence.

According to Bambach, there’s no doubt at all that every 27 million years-odd, huge numbers of species suddenly become extinct. He says this is confirmed by “two modern, greatly improved paleontological datasets of fossil biodiversity” and that “an excess of extinction events are associated with this periodicity at 99% confidence”. This regular mass slaughter has apparently taken place around 18 times, back into the remote past of half a billion years ago. [The Register]

The problem, Nemesis fans, is that the cycle is too precise, the researchers say. If these extinctions result from a dance between our sun and Nemesis, the researchers note, the period of these mass extinctions would change as other stars buffeted the pair and changed the courses of Nemesis’s orbit around the sun.

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When you saw the Hale-Bopp comet, you may have seen material from a distant star passing by. In a new study, a team of astronomers argues that most of the comets that streak through our solar system were actually born in other solar systems.

Given their eccentric orbits and infrequent visits, comets seem like worthy candidates for an exotic origin. But the prevailing thinking said no, they are rather ordinary. Researchers thought most of the comets that pay us a visit initially formed from the sun’s protoplanetary disk—the same swirling mass that formed our own planet—and came to reside in the weird Oort cloud region at the periphery of our solar system. From there, the gravitational bullying of larger bodies can dislodge a few like Halley’s Comet or Hale-Bopp, which swerve into an orbit that sees them visit the inner solar system now and then.

In a study in Science this week, researchers led by Harold Levison posit a different idea: Many of the comets hanging around our solar system are stolen. It goes like this:

Like most stars, the sun may very well have been created in a tightly nestled birth cluster, a stellar nursery with tens, hundreds or possibly even thousands of stars. During millions of years of intimate infancy, the newborn stars could have exchanged vast numbers of comets from the fringes of their disks, each of them winding up with an ensemble of hand-me-downs from their stellar siblings [Scientific American].

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A comet from the deep space far beyond Pluto probably won’t smash into the Earth and obliterate all life, reassuring researchers said today. New calculations have determined that most extinction events that have occurred over our planet’s history probably weren’t caused by killer comet showers, which bodes well for the future, too. The findings are both welcome and well-timed since only last week an object dramatically smashed into Jupiter; many researchers believe the culprit was a comet.

In the new study, published in Science, researchers focused on long-period comets, which are among the wild cards in a thick deck of cosmic threats. In contrast with short-period comets, such as Comet Halley and Comet Tempel-Tuttle, long-period comets trace insanely eccentric orbits that range out beyond Neptune, Pluto and the Kuiper Belt to a little-understood region on the solar system’s edge known as the Oort Cloud [MSNBC]. The Oort cloud, which contains billions of small, icy objects, may extend from about 93 billion miles from the sun to as far as 9 trillion miles away.

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Astronomers have spotted an icy object near Neptune that they say hails from the distant Oort Cloud, the distant reservoir of asteroids that encircles the solar system out beyond the orbit of Pluto. The object, at least 30 miles wide, is on the return leg of a 22,500-year journey around the sun, astronomers announced today [SPACE.com].

The new object is about 60 miles in diameter. “It’s basically a comet, but it never gets close enough to the Sun to develop a long, bright tail of evaporated gas and dust,” [lead researcher Andrew] Becker said in a statement [Reuters]. Researchers say the newly discovered voyager, which is currently going by the unromantic name 2006 SQ372, is the first object ever sighted from the inner Oort Cloud, a region that astronomers know very little about.

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